1. Field of the Invention
The invention relates to a device for raking material from a storage heap.
2. Description of the Prior Art
Material reclamation from a storage heap is often accomplished by raking material from one end face of the heap using a raking device which overlays that end face. This device is mounted on a bridge, which extends parallel to the base line of the end face and which travels in a reciprocating, i.e., back and forth, direction parallel to the end face of the heap.
In a well known arrangement, the raking device is comprised of a triangular harrow which is substantially the same size, i.e., width, as the end surface of the heap. The harrow is capable of performing a reciprocating movement over a short distance along and parallel to the bridge. The inclination of the harrow is set to correspond to the inclination of the end face from which material is to be raked. A hoisting mechanism, preferably constituted by one or more flexible tension elements, such as wire, and pulley blocks, is used to make this adjustment. The flexible tension element emanates from a point situated near the apex of the harrow and is connected to a tower which is fixedly mounted to the bridge. By virtue of the connection between the harrow and the stationary tower, the apex of the harrow describes a circular arc as the base of the harrow reciprocally moves parallel to and along the bridge.
To properly rake material from the entire end face of the heap, the harrow must move in straight line, i.e., linear, fashion across and parallel to the end face of the heap. As long as the width of the harrow is the same as or is larger than that of the end face of the heap, then any movement of the harrow is relatively small compared to the total possible distance through which the harrow can travel. As such, the circular arc described by the apex of the harrow approximates a straight line essentially providing the desired linear movement of the harrow across the end face of the heap.
Oftentimes, however, this linear movement is difficult to attain. This is particularly true whenever the width of the heap is large compared to that of the harrow. For such a case, the harrow is required to move a relatively large distance in order to cover the entire end face of the heap. As such, the movement of the apex of the harrow describes a large arc. Consequently, this movement significantly deviates from being linear. One way to produce linear movement for a relatively large heap is to ensure that the harrow will only move through a relatively small distance. This can be effectuated by continually increasing the size of the harrow such that the width of the harrow is always close to that of the end surface of the heap. However, this solution is quite unrealistic as the harrow would quickly become too large, too expensive and too heavy for it to be practical. Thus, since the size of the harrow will in most instances remain fixed, any movement of the harrow across the end face of the heap increasingly and disadvantageously deviates from being linear as the width of the heap increases.
Furthermore, this deviation is particularly evident whenever the harrow encounters the endface of an annular heap. Since the harrow is unsymmetrical with respect to the heap, i.e., the position of the stationary tower is not aligned with an axis of symmetry of the heap, the deviation resembles a monotonic function of the position of the harrow along the bridge. Specifically, the value of the deviation reaches a maximum at one extreme position of the harrow's movement, i.e., one end of the bridge, and is nearly zero at the other. By contrast, where the heap is straight, the stationary tower can be situated on the axis of symmetry of the storage heap. In this case, the value of the deviation is zero or minimum whenever the harrow is in its center position and takes on a maximum value in either of the two extreme or end positions of the harrow's travel.
Various attempts have been made in the art to compensate for any undesired circular movement of the harrow's apex by extending or shortening the wire connecting the harrow to the stationary tower. To accomplish this, hydraulic cylinders or motors are used for winding in or paying out the wire. These solutions, however, require expensive additional equipment such as motors and synchronizing equipment.